Coating mixtures, method of producing them and their use for coating purposes

ABSTRACT

The invention relates to coating mixtures, containing in the anhydrous state at least one polysiloxane, at least one reactive inorganic filler, at least one inorganic material which is film-forming as melt and at least one reactive (oligo)silane, a process for manufacture and their use.

The invention relates to coating mixtures, containing in the anhydrousstate at least one polysiloxane, at least one reactive inorganic filler,at least one inorganic material which is film-forming as melt and atleast one reactive (oligo)silane, a process for manufacture and theiruse.

A multiplicity of mixtures comprising at least one polysiloxane and atleast one inorganic filler, which are used in a very wide range offields, has been known hitherto. Mixtures consisting of a polysiloxaneresin as polysiloxane and a pigment as filler, so-called pigmentedpolysiloxane resins, are used both as lacquer systems and in coatingtechnology. Both pigmented polysiloxane resins in organic solvents andinorganic coatings of enamel have been used hitherto as heat-resistantcoatings. Pigmented polysiloxane resins only have a good propertyprofile, however, When they are used in organic solvents. Inorganiccoatings of enamel are distinguished by high heat resistance. The factthat they are brittle and only achieve their final properties by meansof stoving at temperatures >400° C. is, however, a disadvantage. Forthis reason they are easily damaged, particularly in the transport phaseand until the necessary temperature has been reached, so that enamelcannot be used as a coating in many fields.

High-temperature-resistant systems have only been achieved hitherto withexclusive use of solvent-based silicone resins, optionally with theaddition of silicone oils as flow control or release agents.Corresponding coatings are composed of the resin as binder, pigments,additives (catalysts, emulsifiers, flow control agents etc.) and varioussolvents. The current aqueous systems have disadvantages, particularlyin respect of their behaviour following drying at room temperature.Unsatisfactory corrosion protection, inadequate hardness and filmstrength (bond strength), drying times which are too long (slurries) andinsufficient storage stability are further disadvantages.

Heat-resistant coatings are chiefly used to protect objects andinstallations of the most varied kind, such as silencers, furnaces,petrochemical industry installations, housings for items of equipment,combustion plants etc.

Examples of the requirements which heat-resistant coatings are expectedto meet are temperature resistance up to 600° C. under long-term andcyclic stress, high resistance at temperature differences (ΔTresistance), high bending strength, colourfastness, resistance tocorrosive effects, good drying properties, good adhesion, simplemanufacturing process (high storage stability) and good handle-abilityand usability in the conventional processes such as spray, roller, dipor brush application.

A high-temperature-resistant corrosion protection coating is producedfor example by drying at room temperature and subsequent stoving.

In mixtures for heat-resistant coatings known hitherto, it was notpossible either to dispense with the use of an organic solvent, orprovide a correspondingly optimized enamel or an optimal combination ofpolysiloxane and enamel.

The object of the invention was therefore to provide stable, low-solventpolysiloxane-based coating mixtures which are as free from organicsolvents as possible, which can be used as heat-resistant coatings inparticular and which are distinguished by an improved property profilecompared with the prior art.

It has now been found that coating mixtures, containing in the anhydrousstate

A) at least one polysiloxane,

B) at least one reactive inorganic filler,

C) at least one inorganic material which is film-forming as melt, and

D) optionally pigments and/or unreactive fillers and

E) at least one reactive (oligo)silane,

F) optionally catalysts and

G) further fillers, in certain proportions, have outstanding propertiescompared with the prior art.

The invention thus provides coating mixtures, containing in theanhydrous state

A) 20 to 40 wt. %, preferably 20 to 35 wt. %, particularly preferably 20to 30 wt. % of at least one polysiloxane,

B) 2 to 30 wt. %, preferably 2 to 20 wt. %, particularly preferably 2 to15 wt. %, most particularly preferably 2 to 10 wt. % and/or 5 to 10 wt.% of at least one reactive inorganic filler,

C) 5 to 50 wt. %, preferably 20 to 40 wt. %, particularly preferably 20to 35 wt. %, most particularly preferably 20 to 30 wt. % of at least oneinorganic material which is film-forming as melt and optionally

D) 0 to 40 wt. %, preferably 1 to 30 wt. %, particularly preferably 3 to20 wt. % of an unreactive filler and/or pigment or a mixture of severalfillers and/or pigments

E) 0.1 to 10 wt. %, preferably 0.5 to 5 wt. %, particularly preferably 1to 3 wt. % of at least one reactive (oligo)silane,

F) 0 to 1 wt. %, preferably 0.01 to 0.5 wt. %, particularly preferably0.01 to 0.3 wt. % of at least one catalyst and

G) 0 to 5 wt. %, preferably 0.1 to 3 wt. % of a further additive or amixture of several additives,

wherein the sum of components A) to G) is 100%.

In the coating mixtures according to the invention, the content of D) ispreferably at least 1 wt. %, that of F), preferably at least 0.05 wt. %.

In the coating mixtures according to the invention, component A) ispreferably at least one hydroxy- and/or alkoxy-functional polysiloxanewhich forms emulsions with water or other solvents in a mixture withwater. Examples of polysiloxanes in the meaning of the invention arecopolymers of polysiloxane and polyester, polyether and/or polyepoxide(and/or their mixtures), as well as linear or branchedorganopolysiloxanes. A polysiloxane resin or a mixture of severalpolysiloxane resins, as described in lines 14-52 of column 3 of EP-A 512418, is preferably used as component A). Particularly preferred arepolysiloxane resins which have a content of 10-80, preferably 20-70,particularly preferably 35-60 wt. % of difunctional structural elementsof the general formula ##STR1## in which

R denotes any organic group with Si-C linkage.

Combinations of branched and linear polysiloxanes are also particularlypreferred.

Component A) is preferably used as aqueous emulsion. The use of A) in anorganic solvent is also possible, but has ecological drawbacks.

Component A) may also, however, be present as a mixture of severalaqueous emulsions. If component A) is used in the form of an aqueousemulsion, the siloxane content is between 5 and 80 wt. %, preferablybetween 10 and 70 wt. %, particularly preferably between 20 and 60 wt.%. Component A) may, however, optionally contain further solvents inaddition to water. In this case at least one emulsifier and/or arheological additive, such as a thickening agent, should preferably beadded. Both cationic and anionic emulsifiers may be used as emulsifiers.Component A) present in the form of an emulsion may contain emulsifiers,thickening agents and also other auxiliary substances in quantities of0.5-15 wt. %, preferably 1-6 wt. %, particularly preferably 1.5-5 wt. %.

Component A) may also contain 0-5 wt. %, preferably 0-2 wt. %,particularly preferably 0-1 wt. % of a bactericide or fungicide as afurther additive. Component A) may consist both of pure polysiloxanesand/or oils and also be present in the form of corresponding emulsionsin water and in a mixture with water and further solvents. Component A)may also additionally contain catalysts. The catalyst content may be upto 1 wt. %, related to component A), wherein conventional condensationcatalysts, such as organotin compounds, organotitanium compounds andorganoaluminium compounds may be used.

In the coating mixtures according to the invention, component B)encompasses all reactive inorganic compounds or inorganic compoundsmodified with organic groups which contain reactive groups and which canreact with themselves and/or other components of the mixtures accordingto the invention. Some examples of component B) are silica sols, alkaliwater glasses, silicic acid esters, organosiliconates, such as sodiummethyl siliconate, titanic acid esters, aluminates, zircon aluminates,aluminium hydroxide and organically modified fillers of all kinds whichcontain reactive group in the above-mentioned meaning of the term, suchas fillers containing epoxy, amino or unsaturated groups, examples ofwhich are quartz, glass, talcum, chalk. The term fillers also includessubstances which are present as solid compounds and/or reaction productsafter the reaction according to the invention. Liquid titanic esters,for example, which are incorporated into the coatings may thus act aseducts.

In the coating mixtures according to the invention, the reactiveinorganic filler B) is preferably colloidal silica in the form of asilica sol, alkali water glasses in aqueous solution or in solid form,alkyl siliconate, aluminium hydroxide or a mixture of these compounds.Sodium or potassium methyl siliconate is particularly preferred as alkylsiliconate. The colloidal silica preferably has a content of 5-60 wt. %of SiO₂, preferably 10-40 wt. % of SiO₂, particularly preferably 15-35wt. % of SiO₂. In a preferred embodiment of the invention B) is acolloidal silica sol with a solids content of 5 to 60 wt. % and/or analkali water glass of sodium, potassium or lithium with a molar ratio ofMe₂ O:SiO₂ >1.2, where Me=Na, K or Li. A reactive inorganic filler inthe meaning of the invention is also pyrogenic silica in powder form andcolloidal silica in the form of silica sols. The silica sol particlesmay also be surface-modified according to the known processes. Modifiedsilica sol, as described in DE-B 2 408 896, U.S. Pat. No. 2,892,797,U.S. Pat. No. 2,574,902, U.S. Pat. No. 2,457,971, U.S. Pat. No.2,668,149 and U.S. Pat. No. 2,650,200, is also preferred as componentB). Silica sols with a particle size of 5-100 nanometers areparticularly preferred, 10-30 nanometers being most particularlypreferred.

In the coating mixtures according to the invention, component C) may beany inorganic material which is film-forming in the melt. The material(C) which is film-forming in the melt is preferably an enamel and/or alow-melting glass.

The following special compositions (in wt. %) are particularly preferredas enamel C) in the meaning of the invention:

    ______________________________________                                        Compound                                                                              Content in wt. %                                                      ______________________________________                                        SiO.sub.2                                                                             25-45                                                                 TiO.sub.2                                                                             10-27                                                                 ZrO.sub.2                                                                              0-10                                                                 P.sub.2 O.sub.5                                                                       0-7                                                                   V.sub.2 O.sub.5                                                                        0-15                                                                 B.sub.2 O.sub.3                                                                        0-15                                                                 Al.sub.2 O.sub.3                                                                      0-5                                                                   R.sub.2 O                                                                             20-38       where R.sub.2 O = Na.sub.2 O 10-20, K.sub.2 O 2-15,                           Li.sub.2 O 0-8                                            RO       0-14       where RO = CaO 0-8, MgO 0-10,                                                 BaO 0-10, ZnO 0-8                                         F.sup.- 0-4                                                                   ______________________________________                                    

These may be mixed up to 10% with colour oxides (Fe₂ O₃, CoO, CuO) andup to 10% of melt-active substances such as SnO, Bi₂ O₃ and MoO₃.

The low-melting glass and/or enamel in the meaning of the inventionshould have a softening point below 600° C., preferably <550° C.,particularly preferably <440° C. but not below 200° C., preferably notbelow 300° C. and particularly preferably not below 350° C. Thecoefficient of thermal expansion of the low-melting glass and/or enamelshould be adapted to that of the metallic substrate, so that thecoatings will not spall on heating. The coefficient of thermal expansionof the low-melting glass and/or enamel should be at least 380×10⁻⁷ /K,preferably >400×10⁻⁷ /K (measured cubically, between 20° C. and 400°C.), wherein a coefficient of expansion greater than 550×10⁻⁷ /K is lesspreferred. When manufacturing, processing and also using the glassand/or enamel, the use of low-melting physiologically unacceptable ortoxic elements, such as lead, cadmium, is less preferred. To produce theenamels and/or glasses according to the invention, common commercialenamel raw materials such as borax (Na₂ B₄ O₇ ×5H₂ O), ground quartz,sodium polyphosphate, feldspar, zircon sand, fluorspar, alkali andalkaline earth carbonates, titanium dioxide, vanadium pentoxide andoptionally colour oxides (Fe₂ O₃, MnO, CoO, CuO etc.) are melted attemperatures of 1100 to 1260° C. and quenched over water-cooled rollers.The flakes thus produced are then milled either dry, or wet usingvarious mill additives and further processed. Milling auxiliarysubstances such as glycols, silicone oils or the like may optionally beused when dry-milling.

Component D) in the meaning of the invention is preferably a pigment,iron oxide and/or a mica. Particularly preferred as component D) is apigment or filler in the form of an inorganic, organic and/or metallicsubstance or mixtures thereof, such as aluminium oxide, phosphatesand/or carbonates, carbides of magnesium and calcium, nitrides,magnesium oxide, aluminium hydroxide, titanium dioxide, silicon carbide,zinc oxide, aluminium bronze, tin and zinc dust, zinc phosphate,phthalocyanine blue, various spinels, carbon black, graphite etc. Mostparticularly preferably D) are inorganic thermostable pigments and/or atleast one inorganic filler, such as iron oxide, mica and titaniumdioxide.

Component E) in the meaning of the invention preferably comprises(oligo)silanes and/or (partial) hydrolyzates thereof and/or mixtures ofdifferent (oligo)silanes and/or (partial) hydrolyzates thereof. They maybe present in the form of their aqueous solutions and/or emulsions ordispersions. Solutions of component E) in water are most particularlypreferred. Water-soluble partial hydrolyzates of functional silanes,e.g. silanes containing amino groups, epoxy and/or hydroxyl groups, suchas 3-aminopropyl trisalkoxysilane, epoxypropyl trisalkoxysilane,3-hydroxypropyl trisalkoxysilane, and silanes containing carboxyl groupsmay be mentioned as preferred component E).

Those catalysts which accelerate condensation reactions are preferablyconsidered at component F). Catalysts for the reaction of hydroxylgroups in silanols and/or for the reaction of silanols withalkoxy-silane groups, such as organometallic compounds of tin, areparticularly preferred. Typical examples of component F are dibutyltindilaurate or dibutyltin dioctoate.

Component G) may also be any additive which is known for the manufactureof lacquers and paints, such as fillers and pigments, mica, lacqueradditives such as dispersing, flow control, thickening, de-foamingagents and other auxiliary substances, fungicides, bactericides,stabilizers, inhibitors and catalysts. G) may, however, also be apolymer or a mixture of several polymers, such as cellulose, polyether,polyacrylates, polyurethanes, plasticizers and various inorganic resins.

As component G) the coating mixtures according to the invention may alsocontain organic, organometallic and/or inorganic corrosion inhibitors,such as phosphoric acid derivatives, various amines, substituted benzenetriazoles, nitrosophthalic acid salts, Talmin, zinc salts of organicacids of nitrogen such as Alcophor®827, (Henkel), substituted phenols orthe like, or also wetting agents.

The invention also provides coating mixtures obtainable by:

presenting 2 to 30 wt. %, preferably 2 to 20 wt. %, particularlypreferably 2 to 15 wt. %, most particularly preferably 5 to 10 wt. %, ofat least one component B) as aqueous dispersion,

stirring in 0 to 5 wt. %, preferably 0.01 to 0.5 wt. %, particularlypreferably 0.1 to 0.3 wt. % of wetting agent (component G), 0 to 40 wt.%, preferably 1 to 40 wt. %, particularly preferably 1 to 30 wt. %, mostparticularly preferably 3 to 20 wt. %, of component D), 5 to 50 wt. %,preferably 20 to 40 wt. %, particularly preferably 20 to 35 wt. %, mostparticularly preferably 20 to 30 wt. % of at least one component C),

then adding 0.1 to 10 wt. %, preferably 0.5 to 10 wt. %, particularlypreferably 1 to 10 wt. %, most particularly preferably 1 to 3 wt. % ofat least one reactive (oligo)siloxane (component E) and optionallyfurther components G) accompanied by stirring and

adding 20 to 40 wt. %, preferably 20 to 35 wt. %, particularlypreferably 20 to 30 wt. % of at least one component A) and 0 to 1 wt. %,preferably 0.01 to 0.5 wt. %, particularly preferably 0.01 to 0.3 wt. %of component F) and optionally further components G), wherein the sum ofall components G) is. 0 to 5 wt. %, accompanied by stirring.

The invention also provides a process for the manufacture of the coatingmixtures according to the invention, according to which, in thequantities according to the invention:

component B) is presented as aqueous dispersion,

optionally wetting agent as component G), optionally non-reactiveinorganic pigments, fillers and at least one component C) are stirredinto the aqueous dispersion of component B) and are then mixedpreferably for 5 to 60 minutes,

component E) and optionally further components G) are added accompaniedby stirring and then at least one component A) and optionally componentF) as well as optionally further components G), wherein the sum of allcomponents G) is 0 to 5 wt. %, are metered in accompanied by stirring.

It is particularly preferred that the coating mixtures be manufacturedby the process according to the invention. This process improves boththe properties of the coatings and the quality of the lacquers/paintsfrom which the coatings according to the invention are produced.

In a particularly preferred embodiment of the invention, in thequantities according to the invention:

1) aqueous silica sol is presented as component B), after which

2) in the sequence which follows, wetting agent (component G)),non-reactive inorganic pigments (component D)) and component C) areadded accompanied by stirring and then intensively dispersed for 5 to 60minutes, preferably 10 to 30 minutes,

3) reactive (oligo)silane comprising 3-aminopropyl trisethoxysilane(component E)) and optionally further components G) are then addedaccompanied by stirring and dispersed for 5 to 60 minutes, preferably 10to 30 minutes and

4) finally, component A) and optionally catalyst (component F)) andoptionally further components G), wherein the sum of all components G)is 0 to 5 wt. %, are added and stirred for 5 to 60 minutes, preferably10 to 30 minutes.

The methods used to produce lacquers, such as ball mills and otherintensive mixing processes, are preferred for producing the dispersionscomprising components A) to F). The use of various auxiliary substances,particularly dispersing agents, such as polyacrylic acid derivatives,polyphosphates, phosphonocarboxylic acid derivatives, is preferred inthe production of these coating mixtures. To stabilize the coatingsystems according to the invention and their components and to protectagainst sedimentation, various organic and inorganic compounds, such asbentonite, celluloses, polyacrylates or polyurethane thickeners, may beused.

The dispersions comprising the mixtures according to the inventioncontain 20-90 wt. %, preferably 40-80 wt. %, particularly preferably50-70 wt. % of solids. The aqueous phase may optionally contain organicsolvents.

The invention also provides a process for the manufacture of coatingsfrom the coating mixtures according to the invention, wherein thecoating mixtures are applied to the material to be coated, optionallypre-dried at room temperature and then exposed to temperatures of 150 to750° C., preferably 150 to 700° C., for 1 to 120 minutes. The coatingmixtures are preferably used in the form of an aqueous dispersion.

Virtually all heat-resistant substances, such as steel, aluminium andalso other metals and their alloys, enamelled materials and metal-coatedsteels, may be used as materials to be coated. These materials may beused with or without pre-treatment depending on type and field ofapplication. Any pre-treatment may be carried out by all known methods,such as abrasive blasting treatment.

The coating mixtures according to the invention are preferably appliedto a solid substrate by spray, dip, roller and brush applicationmethods. Coatings with film thicknesses of 5-300 μm, preferably 10-150μm, particularly preferably 15-75 μm, may be produced in this wayaccording to requirements.

The coating mixtures applied may also be pre-dried at highertemperatures. As a coating on the solid substrate, the coating mixturespre-dried at room temperature already have sufficient mechanicalstrength to be transported, deformed and handled in other ways, but thefinal applicational properties are only achieved after heat treatment.In this case, short-term treatment at higher temperature or, by analogy,a longer period of treatment at low temperature may be carried out. Thepreferred temperature range is between 150 and 700° C., preferablybetween 200 and 600° C. The duration of the heat treatment may bebetween 1 and 120 minutes, preferably 5-60 minutes.

The invention also provides the use of the coating mixtures according tothe invention for the heat-resistant coating of furnaces, silencers,industrial plants and objects of all kinds which are exposed to heat.Depending on prior heat treatment, these heat-resistant coatingsrepresent soft to very hard films and differ fundamentally, as far astheir properties are concerned, from those of the raw materials usedsince these were selected in such a way that they can react together todifferent degrees depending on the temperature range. The propertyprofile of the coatings produced depends very considerably on thetemperature selected. It is therefore possible to produce tailor-madecoatings for each field of application on the basis of temperature.

The coatings according to the invention are chiefly distinguished byhigh resistance to bending, temperature and temperature difference, andresistance to corrosion, as the examples below demonstrate.

EXAMPLES

The following substances are used in the examples:

I) as polysiloxanes:

Ia) 47% aqueous emulsion of a hydroxyfunctional methyl silicone resin ofaverage composition T₂₁₀ D₂₃ M₄ with an average molecular weight ofapprox. 12,000

II) as reactive inorganic fillers:

IIa) 30% aqueous colloidal silica suspension with a BET surface of 100m² /g and a pH value of 10

III) as enamel:

IIIa) VP-AI 61-1167 M: enamel frit, Messrs Email Brugge

IIIb) AT 6115®: enamel frit, Messrs Email Brugge

IV) as pigments:

IVa) Bayferrox 303T®: black iron oxide, Messrs Bayer AG

IVb) Echtschwarz®: black spinel, Messrs Bayer AG

V) as (oligo)silane:

Va) aminopropyl trisethoxysilane, 20% in water

VI) as catalyst:

VIa) 10% aqueous emulsion of dibutyltin dilaurate

VII) as liquefier:

VIla) Bayhibit S®: sodium salt of a trifunctional phosphonocarboxylicacid, Messrs Bayer AG

Comparative Example 1

Specification for producing the coating material (for quantities seeTable 1, for test results see Table 2):

Water is presented and components IIIb, IVa and IVb are addedaccompanied by stirring, and stirred with the dissolver at approx. 1000rpm. Component VII is then added and stirring continues for 60 minutesat 1800 rpm. This aqueous slurry is then added to the pre-mixedcomponents I and IIa. The mixture is then stirred for 10 minutes at 1800rpm.

Example 1a (According to the Invention)

Production process as Comparative example 1, but with the compositionshown in Table 1; f or test results see Table 2:

Examples 2a to 2g

General specification for producing the coating material according tothe invention (for quantities see Table 1, for test results see Table2):

1) component IIa is presented, after which

2) in the sequence which follows, component VII, components IV andcomponent III are added accompanied by stirring and then intensivelydispersed for 20 minutes at approx. 3000 rpm,

3) component IIb is then added accompanied by stirring and dispersed for20 minutes,

4) finally, component I and component VI are added and stirringcontinues for 20 minutes.

                                      TABLE 1                                     __________________________________________________________________________    Weighed portions of the components in content by weight                       quantities in wt. % related to dry substance are quoted in brackets           Ex. No.                                                                       Components                                                                          1*  1a  2a  2b  2c  2d  2e  2f  2g                                      __________________________________________________________________________    Ia    56.30                                                                             53.40                                                                             53.40                                                                             42.55                                                                             53.40                                                                             53.40                                                                             42.55                                                                             64.89                                                                             53.40                                         (26.46)                                                                           (25.10)                                                                           (25.10)                                                                           (20.00)                                                                           (25.10)                                                                           (25.10)                                                                           (20.00)                                                                           (30.50)                                                                           (25.10)                                 IIa   27.00                                                                             35.33                                                                             35.33                                                                             52.33                                                                             35.33                                                                             35.33                                                                             29.33                                                                             17.33                                                                             35.33                                         (8.10)                                                                            (10.60)                                                                           (10.60)                                                                           (15.70)                                                                           (10.60)                                                                           (10.60)                                                                           (8.8)                                                                             (5.2)                                                                             (10.60)                                 IIIa                                  15.34                                                                         (15.34)                                 IIIb  32.50                                                                             30.68                                                                             30.68                                                                             30.68                                                                             40.00                                                                             21.00                                                                             30.68                                                                             30.68                                                                             15.34                                         (32.50)                                                                           (30.68)                                                                           (30.68)                                                                           (30.68)                                                                           (40.00)                                                                           (21.00)                                                                           (30.68)                                                                           (30.68)                                                                           (15.34)                                 IVa   16.25                                                                             15.30                                                                             15.30                                                                             15.30                                                                             11.14                                                                             20.14                                                                             15.30                                                                             15.30                                                                             15.30                                         (16.25)                                                                           (15.30)                                                                           (15.30)                                                                           (15.30)                                                                           (11.1)                                                                            (20.14)                                                                           (15.30)                                                                           (15.30)                                                                           (15.30)                                 IVb   16.25                                                                             15.30                                                                             15.30                                                                             15.30                                                                             11.14                                                                             20.14                                                                             15.30                                                                             15.30                                                                             15.30                                         (16.25)                                                                           (15.30)                                                                           (15.30)                                                                           (15.30)                                                                           (11.14)                                                                           (20.14)                                                                           (15.30)                                                                           (15.30)                                                                           (15.30)                                 V         11.50                                                                             11.50                                                                             11.50                                                                             11.50                                                                             11.50                                                                             47.50                                                                             11.50                                                                             11.50                                             (2.30)                                                                            (2.30)                                                                            (2.30)                                                                            (2.30)                                                                            (2.30)                                                                            (9.50)                                                                            (2.30)                                                                            (2.30)                                  VIa       0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                                                              0.20                                              (0.02)                                                                            (0.02)                                                                            (0.02)                                                                            (0.02)                                                                            (0.02)                                                                            (0.02)                                                                            (0.02)                                                                            (0.02)                                  VIIa  0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                                          (0.40)                                                                            (0.40)                                                                            (0.40)                                                                            (0.40)                                                                            (0.40)                                                                            (0.40)                                                                            (0.40)                                                                            (0.40)                                                                            (0.40)                                  Water 43.60                                                                             7.64                                                                              7.64    7.64                                                                              7.64    15.00                                                                             7.64                                    __________________________________________________________________________     *Comparative example                                                     

                                      TABLE 2                                     __________________________________________________________________________    Test results                                                                            Examples                                                                      1                                                                   Tests     Comp.                                                                             1a  2a 2b 2c 2d 2e 2f 2g                                        __________________________________________________________________________    Drying at RT/mins.                                                            Dust-free 15  15  10 10 15 10 10 15 10                                        Tack-free 30  30  25 20 25 25 20 30 25                                        Temperature stress                                                            1 hr/200° C.                                                                      0   0   0  0  0  0  0  0  0                                        1 hr/400° C.                                                                      0   0   0  0  0  0  0  0  0                                        1 hr/600° C.                                                                      0   0   0  0  0  0  0  0  0                                        Temperature shock test                                                        600° C./RT                                                                        0   5   0 10  0 10  5 10  0                                        Salt spray test                                                               after thermal stress                                                          RT        Ri3-4                                                                             Ri2-3                                                                             Ri0                                                                              Ri3                                                                              Ri3                                                                              Ri2                                                                              Ri3                                                                              Ri0                                                                              Ri0                                       1 hr/200° C.                                                                     Ri3-4                                                                             Ri3 Ri0                                                                              Ri3                                                                              Ri3                                                                              Ri1                                                                              Ri3                                                                              Ri1                                                                              Ri0                                       1 hr/400° C.                                                                     Ri1 Ri1 Ri0                                                                              Ri1                                                                              Ri1                                                                              Ri0                                                                              Ri1                                                                              Ri1                                                                              Ri0                                       1 hr/600° C.                                                                     Ri0 Ri0 Ri0                                                                              Ri0                                                                              Ri0                                                                              Ri0                                                                              Ri0                                                                              Ri0                                                                              Ri0                                       __________________________________________________________________________

Measured variables and test conditions for evaluating heat-resistantcoatings:

Temperature stress:

The measured variable is the spalled film portion in % after heattreatment at a specified time and temperature.

Temperature shock test:

The coated and pre-dried panel is exposed to a temperature of 600° C.for 1 hour and then directly quenched in 20° C. cold water. Measuredvariable: spalled film portion in %.

Salt spray test:

Measured variable: rust value to DIN 53 210; the comparative examplesand other coatings which already exhibited spalled areas after heattreatment were not tested. The measured values have the followingmeaning:

    ______________________________________                                        Abbreviation  rusted surface, %                                               ______________________________________                                        Ri0 =         0                                                               Ri1 =         0.05                                                            Ri2 =         0.5                                                             Ri3 =         1                                                               Ri4 =         8                                                               ______________________________________                                    

What is claimed is:
 1. Water-thinable coating mixtures, containing inthe anhydrous stateA) 20 to 40 wt. % of at least one polysiloxane, B) 2to 30 wt. % of at least one colloidal silica, C) 5 to 50 wt. % of atleast one low-melting enamel having a melting point of 300° C.-700° C.and optionally D) 0 to 40 wt. % of one or more unreactive fillers or acombination thereof, E) 0.1 to 10 wt. % of at least one reactive(oligo)silane, F) 0 to 1 wt. % of at least one catalyst and G) 0 to 5wt. % of a further additive or a mixture of several additives,whereinthe sum of components A) to G) is 100%.
 2. Water thinable coatingmixtures according to claim 1, wherein component A) is at least onehydroxy- or alkoxy-functional polysiloxane, or a combination of both,which forms emulsions with water or other solvents in a mixture withwater.
 3. Water thinable coating mixtures according to claim 1, whereinthe reactive inorganic filler B) is colloidal silica in the form of asilica sol.
 4. Water thinable coating mixtures according to claim 1,wherein the reactive inorganic filler B) is colloidal silica sol with asolids content of 5 to 60 wt. %.
 5. Coating mixtures according to claim1, wherein the inorganic material C) which is film-forming as melt is atleast one enamel, one low-melting glass or a combination thereof. 6.Water thinable coating mixtures according to claim 1, wherein thereactive (oligo)silane E) is a (partial) hydrolyzate of 3-aminopropyl-,1,2-epoxypropyl, 3-hydroxypropyl trisalkoxysilane or a combinationthereof.
 7. Water thinable coating mixtures according to claim 1,wherein the further additives G) are pigments, iron oxides, mica or acombination thereof.
 8. Water thinable coating mixtures according toclaim 1, wherein the content of F) is at least 0.05 wt. %.
 9. Waterthinable coating mixtures obtainable by:presenting 2 to 30 wt. % of atleast one component B) as aqueous dispersion, stirring in 0 to 5 wt. %of wetting agents as component G), 0 to 40 wt. % of component D) and 5to 50 wt. % of at least one component C) accompanied by stirring andoptionally subsequent stirring for 5 to 60 minutes. then adding 0.1 to10 wt. % of at least one component E) optionally further components G)accompanied by stirring and adding 20 to 40 wt. % of at least onecomponent A) and 0 to 1 wt. % of component F) and optionally furthercomponents G), wherein the sum of all components G) is 0 to 5 %,accompanied by stirring.
 10. Process for the manufacture of the waterthinable coating mixtures of claim 1, wherein2 to 30 wt. % of at leastone component B) is presented as aqueous dispersion, 0 to 5 wt. % ofwetting agent, 0 to 40 wt. % of component D) and 5 to 50 wt. % of atleast one component C) are stirred into the aqueous dispersion ofcomponent B), 0.1 to 1 wt. % of at least one component E) and optionallyfurther components G) are added accompanied by stirring and then 20 to40 wt. % of at least one component A) and 0 to 1 wt. % of component F)and 0 to 5 wt. % of component G), wherein the sum of all components G)is 0 to 5 wt. %, are metered in accompanied by stirring.
 11. Process forthe manufacture of coatings from water thinable coating mixturesaccording to claim 1, wherein the mixture is applied to the material tobe coated, optionally pre-dried at room temperature and then exposed totemperatures of 150 to 750° C. for 1 to 120 minutes.
 12. A heatresistant coating for furnaces, silencers, industrial plants and objectswhich are exposed to heat, comprising the water thinable coating mixtureof claim 1.